From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751158AbdKTJkh (ORCPT ); Mon, 20 Nov 2017 04:40:37 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51386 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751106AbdKTJkg (ORCPT ); Mon, 20 Nov 2017 04:40:36 -0500 Subject: Re: [PATCH] KVM: VMX: Fix rflags cache during vCPU reset To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Wanpeng Li , Nadav Amit , Dmitry Vyukov References: <1511169423-15671-1-git-send-email-wanpeng.li@hotmail.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Mon, 20 Nov 2017 10:40:33 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <1511169423-15671-1-git-send-email-wanpeng.li@hotmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Mon, 20 Nov 2017 09:40:36 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20.11.2017 10:17, Wanpeng Li wrote: > From: Wanpeng Li > > Reported by syzkaller: > > *** Guest State *** > CR0: actual=0x0000000080010031, shadow=0x0000000060000010, gh_mask=fffffffffffffff7 > CR4: actual=0x0000000000002061, shadow=0x0000000000000000, gh_mask=ffffffffffffe8f1 > CR3 = 0x000000002081e000 > RSP = 0x000000000000fffa RIP = 0x0000000000000000 > RFLAGS=0x00023000 DR7 = 0x0000000000000002 > .......................... > ------------[ cut here ]------------ > WARNING: CPU: 6 PID: 24431 at /home/kernel/linux/arch/x86/kvm//x86.c:7302 kvm_arch_vcpu_ioctl_run+0x651/0x2ea0 [kvm] > CPU: 6 PID: 24431 Comm: reprotest Tainted: G W OE 4.14.0+ #26 > RIP: 0010:kvm_arch_vcpu_ioctl_run+0x651/0x2ea0 [kvm] > RSP: 0018:ffff880291d179e0 EFLAGS: 00010202 > Call Trace: > ? synchronize_rcu.part.59+0x9b/0xf0 > ? synchronize_rcu_expedited+0xa0/0xa0 > ? kfree_call_rcu+0x20/0x20 > ? trace_raw_output_rcu_utilization+0x70/0x70 > ? kvm_arch_vcpu_runnable+0x220/0x220 [kvm] > ? wait_for_completion+0x222/0x2a0 > ? __wait_rcu_gp+0x1d3/0x230 > ? kvm_vcpu_ioctl+0x479/0x880 [kvm] > kvm_vcpu_ioctl+0x479/0x880 [kvm] > ? kvm_dev_ioctl+0xba0/0xba0 [kvm] > ? pick_next_task_fair+0x629/0xce0 > ? sched_clock+0x1b/0x20 > ? check_chain_key+0x131/0x1e0 > ? lock_acquire+0x2c0/0x2c0 > ? check_flags.part.44+0x62/0x250 > ? check_chain_key+0x131/0x1e0 > ? __lock_acquire+0xd2e/0x1cb0 > do_vfs_ioctl+0x142/0x9a0 > ? ioctl_preallocate+0x150/0x150 > ? lock_acquire+0x2c0/0x2c0 > ? lock_acquire+0x118/0x2c0 > ? __lock_is_held+0x4b/0xe0 > ? __fget+0x16a/0x250 > SyS_ioctl+0x74/0x80 > entry_SYSCALL_64_fastpath+0x23/0x9a > > The syzkaller testcase tries to setup the processor specific debug registers > and configure vCPU for handling guest debug events through KVM_SET_GUEST_DEBUG. > The KVM_SET_GUEST_DEBUG ioctl will get and set rflags in order to set TF bit > if single step is needed. All regs' caches are reset to avail and GUEST_RFLAGS > vmcs field is reset to 0x2 during vCPU reset. However, the cache of rflags is > not reset during vCPU reset. The function vmx_get_rflags() returns an unreset > rflags cache value since the cache is marked avail, it is 0 after boot. Vmentry > fails if the rflags reserved bit 1 is 0. > > This patch fixes it by resetting both the GUEST_RFLAGS vmcs field and its cache > to 0x2 during vCPU reset. > > Reported-by: Dmitry Vyukov > Cc: Paolo Bonzini > Cc: Radim Krčmář > Cc: Nadav Amit > Cc: Dmitry Vyukov > Signed-off-by: Wanpeng Li > --- > arch/x86/kvm/vmx.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index b348920..131fa1c 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -5590,6 +5590,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) > vmcs_write64(GUEST_IA32_DEBUGCTL, 0); > } Indeed, looks like the right think to do when looking at vmx_set_rflags(). Reviewed-by: David Hildenbrand > > + vmx->rflags = 0x02; > vmcs_writel(GUEST_RFLAGS, 0x02); > kvm_rip_write(vcpu, 0xfff0); > > -- Thanks, David / dhildenb